the name might well ba a "play" on a word.I encountered that name (pronounced Sierran) a long time ago in West Virginia. The residents of the area were descendants of what were called Scotch-Irish, Welsh and some Irish who fled Ireland because the potato famine. I never thought too much of it at the time Until I met Two other families from west Virginia, One with a daughter named Ciara(Sierra) and the other with a son named Ciarin(Ciarin). I think the spelling was corrupted by Immigration officials as has happened so often.